Known, from the Polish patent description No. 174172, is a propulsion mechanism, especially for a bicycle, equipped with two, oscillatingly mounted on a joint axis, rear-facing arms ended with pedals, and where on the hub of the bicycle's drive wheel mounted are two freewheels and to each of the arms fitted is rotatively one end of one of the two chains connecting this arm with one of two freewheels fitted on the hub of the bicycle drive wheel, and the other ends of chains are mutually joined with a flexible connector run on a reversible wheel.